This invention relates to a laminate particularly for a security application and more specifically to such a laminate which includes a plasticized sheet containing polyvinyl butyral (PVB).
Laminated glazings containing an impact-absorbing plastic layer are known for use as vehicle and building windows, skylights and the like. One form of such glazing is used in security applications such as prison windows, retail (jewelry) casings, bullet and burglar-resistant doors and windows for airport checkpoints, storefronts, witness (courtroom) protection and the like. A security glazing includes one or more layers of clear polycarbonate (PC) to significantly increase impact resistance. Since PC is susceptible to atmospheric degradation, security glazings preferably also include one or more glass layers to protect the PC. Since PC does not adhere well to glass, an interlayer between the PC and glass is used which adheres well to both the glass and PC. Plasticized PVB qualifies as such an interlayer but plasticizers traditionally used with PVB are known to stress crack or craze (minute surface cracks) PC which causes haze in the laminate and destroys its optical properties. Consequently, it is further known (see e.g. U.S. Pat. Nos. 4,128,694 and 4,514,464) to use a plasticizer for PVB which does not damage PC when the two are in laminating contact. Though PC-resistant plasticizers for PVB are known, their efficacy in avoiding stress cracking could be improved.